To tread on ∨ upon. (a) To trample; to set the foot on in contempt. "Thou shalt tread upon their high places." Deut. xxxiii. 29. (b) to follow closely. "Year treads on year." Wordsworth. -- To tread upon the heels of, to follow close upon. "Dreadful consequences that tread upon the heels of those allowances to sin." Milton.